This invention relates to an amorphous silicon solar cell and a method of its manufacture, and in particular to a method of manufacture of a see-through type amorphous silicon solar cell or an integrated type amorphous silicon solar cell,
An amorphous silicon solar cell is fabricated by forming thin layers of a transparent electrode, amorphous silicon, and backside electrode on a substrate. Vacuum evaporated aluminum with a film thickness of of 0.3 to 1 .mu.m is principally used for the backside electrode. A single cell of this type of solar cell has a voltage of 1 Volt or less. A plurality of cells can be connected in series to attain a prescribed voltage. The integrated type solar cell has been developed for connecting a plurality of cells in series. In this type of solar cell, a patterning process is used to pattern the transparent electrode, amorphous silicon (subsequently referred to as a-Si) layer, and backside electrode
A see-through type solar cell, provided with grooves and perforations, that passes part of the incident light has been developed. The method of manufacturing the see-through type solar cell includes forming thin layers of transparent electrode film, photovoltaic layer, and metallic layer backside electrode on a transparent substrate. Next, resist with a pattern of openings is formed on the metallic electrode layer, and holes and grooves are etched through the metallic electrode layer and then through the photovoltaic layer.
In this method, when the metallic layer backside electrode is etched, it is done by `wet-etching` using an etching solution. However, when the photovoltaic layer is etched, it is done by `dry-etching` normally using a plasma discharge of CF.sub.4 gas.
However, in the fabrication method described above, after wet-etching the metallic electrode layer, the photovoltaic layer must be dry-etched. Therefore, the extremely troublesome operation of reloading substrates, from the cassette used for wet-etching the metallic electrode layer, into the tray used for dry-etching, must be performed. Further, since moisture remaining on the substrate after wet-etching must be sufficiently removed before insertion into the dry-etching apparatus, a long drying time is required. Still further, the vacuum system dry-etching apparatus is extremely expensive and is only capable of a limited through-put.
The first primary object of the present invention is to solve the above mentioned problems and provide an inexpensive method of manufacturing large quantities of amorphous silicon solar cells.
Unfortunately, an amorphous silicon solar cell with an aluminum backside electrode cannot be patterned by wet-etching. The reason for this is that an aluminum backside electrode is etched away by NaOH or other alkaline solutions used to etch the a-Si layer. This drawback is avoided by using an alkali resistant metal for the backside electrode. Cu (copper) and Ag (silver) are alkali resistant metals. Metals such as Cu and Ag have high light reflectivity, and reflect light that penetrates through the a-Si layer to improve the solar cell's I.sub.sc (short circuit current) and P.sub.max (maximum power output). However, these metals have the drawback that they do not strongly bond with the a-Si layer and have not been of practical use in the manufacturing environment.
The second primary object of the present invention is to provide an inexpensive, efficient method of mass producing amorphous silicon solar cells in which the backside electrode is strongly bonded to the a-Si layer.